2 * Copyright 2013 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_IO_IOBUF_H_
18 #define FOLLY_IO_IOBUF_H_
20 #include <glog/logging.h>
29 #include <type_traits>
31 #include <boost/iterator/iterator_facade.hpp>
33 #include "folly/FBString.h"
34 #include "folly/Range.h"
35 #include "folly/FBVector.h"
37 // Ignore shadowing warnings within this file, so includers can use -Wshadow.
38 #pragma GCC diagnostic push
39 #pragma GCC diagnostic ignored "-Wshadow"
44 * An IOBuf is a pointer to a buffer of data.
46 * IOBuf objects are intended to be used primarily for networking code, and are
47 * modelled somewhat after FreeBSD's mbuf data structure, and Linux's sk_buff
50 * IOBuf objects facilitate zero-copy network programming, by allowing multiple
51 * IOBuf objects to point to the same underlying buffer of data, using a
52 * reference count to track when the buffer is no longer needed and can be
59 * The IOBuf itself is a small object containing a pointer to the buffer and
60 * information about which segment of the buffer contains valid data.
62 * The data layout looks like this:
70 * +------------+--------------------+-----------+
71 * | headroom | data | tailroom |
72 * +------------+--------------------+-----------+
74 * buffer() data() tail() bufferEnd()
76 * The length() method returns the length of the valid data; capacity()
77 * returns the entire capacity of the buffer (from buffer() to bufferEnd()).
78 * The headroom() and tailroom() methods return the amount of unused capacity
79 * available before and after the data.
85 * The buffer itself is reference counted, and multiple IOBuf objects may point
86 * to the same buffer. Each IOBuf may point to a different section of valid
87 * data within the underlying buffer. For example, if multiple protocol
88 * requests are read from the network into a single buffer, a separate IOBuf
89 * may be created for each request, all sharing the same underlying buffer.
91 * In other words, when multiple IOBufs share the same underlying buffer, the
92 * data() and tail() methods on each IOBuf may point to a different segment of
93 * the data. However, the buffer() and bufferEnd() methods will point to the
94 * same location for all IOBufs sharing the same underlying buffer.
96 * +-----------+ +---------+
97 * | IOBuf 1 | | IOBuf 2 |
98 * +-----------+ +---------+
100 * data | tail |/ data | tail
102 * +-------------------------------------+
104 * +-------------------------------------+
106 * If you only read data from an IOBuf, you don't need to worry about other
107 * IOBuf objects possibly sharing the same underlying buffer. However, if you
108 * ever write to the buffer you need to first ensure that no other IOBufs point
109 * to the same buffer. The unshare() method may be used to ensure that you
110 * have an unshared buffer.
116 * IOBuf objects also contain pointers to next and previous IOBuf objects.
117 * This can be used to represent a single logical piece of data that its stored
118 * in non-contiguous chunks in separate buffers.
120 * A single IOBuf object can only belong to one chain at a time.
122 * IOBuf chains are always circular. The "prev" pointer in the head of the
123 * chain points to the tail of the chain. However, it is up to the user to
124 * decide which IOBuf is the head. Internally the IOBuf code does not care
125 * which element is the head.
127 * The lifetime of all IOBufs in the chain are linked: when one element in the
128 * chain is deleted, all other chained elements are also deleted. Conceptually
129 * it is simplest to treat this as if the head of the chain owns all other
130 * IOBufs in the chain. When you delete the head of the chain, it will delete
131 * the other elements as well. For this reason, prependChain() and
132 * appendChain() take ownership of of the new elements being added to this
135 * When the coalesce() method is used to coalesce an entire IOBuf chain into a
136 * single IOBuf, all other IOBufs in the chain are eliminated and automatically
137 * deleted. The unshare() method may coalesce the chain; if it does it will
138 * similarly delete all IOBufs eliminated from the chain.
140 * As discussed in the following section, it is up to the user to maintain a
141 * lock around the entire IOBuf chain if multiple threads need to access the
142 * chain. IOBuf does not provide any internal locking.
148 * When used in multithread programs, a single IOBuf object should only be used
149 * in a single thread at a time. If a caller uses a single IOBuf across
150 * multiple threads the caller is responsible for using an external lock to
151 * synchronize access to the IOBuf.
153 * Two separate IOBuf objects may be accessed concurrently in separate threads
154 * without locking, even if they point to the same underlying buffer. The
155 * buffer reference count is always accessed atomically, and no other
156 * operations should affect other IOBufs that point to the same data segment.
157 * The caller is responsible for using unshare() to ensure that the data buffer
158 * is not shared by other IOBufs before writing to it, and this ensures that
159 * the data itself is not modified in one thread while also being accessed from
162 * For IOBuf chains, no two IOBufs in the same chain should be accessed
163 * simultaneously in separate threads. The caller must maintain a lock around
164 * the entire chain if the chain, or individual IOBufs in the chain, may be
165 * accessed by multiple threads.
168 * IOBuf Object Allocation/Sharing
169 * -------------------------------
171 * IOBuf objects themselves are always allocated on the heap. The IOBuf
172 * constructors are private, so IOBuf objects may not be created on the stack.
173 * In part this is done since some IOBuf objects use small-buffer optimization
174 * and contain the buffer data immediately after the IOBuf object itself. The
175 * coalesce() and unshare() methods also expect to be able to delete subsequent
176 * IOBuf objects in the chain if they are no longer needed due to coalescing.
178 * The IOBuf structure also does not provide room for an intrusive refcount on
179 * the IOBuf object itself, only the underlying data buffer is reference
180 * counted. If users want to share the same IOBuf object between multiple
181 * parts of the code, they are responsible for managing this sharing on their
182 * own. (For example, by using a shared_ptr. Alternatively, users always have
183 * the option of using clone() to create a second IOBuf that points to the same
184 * underlying buffer.)
186 * With jemalloc, allocating small objects like IOBuf objects should be
187 * relatively fast, and the cost of allocating IOBuf objects on the heap and
188 * cloning new IOBufs should be relatively cheap.
191 // Is T a unique_ptr<> to a standard-layout type?
192 template <class T, class Enable=void> struct IsUniquePtrToSL
193 : public std::false_type { };
194 template <class T, class D>
195 struct IsUniquePtrToSL<
196 std::unique_ptr<T, D>,
197 typename std::enable_if<std::is_standard_layout<T>::value>::type>
198 : public std::true_type { };
199 } // namespace detail
205 typedef ByteRange value_type;
206 typedef Iterator iterator;
207 typedef Iterator const_iterator;
209 typedef void (*FreeFunction)(void* buf, void* userData);
212 * Allocate a new IOBuf object with the requested capacity.
214 * Returns a new IOBuf object that must be (eventually) deleted by the
215 * caller. The returned IOBuf may actually have slightly more capacity than
218 * The data pointer will initially point to the start of the newly allocated
219 * buffer, and will have a data length of 0.
221 * Throws std::bad_alloc on error.
223 static std::unique_ptr<IOBuf> create(uint32_t capacity);
226 * Allocate a new IOBuf chain with the requested total capacity, allocating
227 * no more than maxBufCapacity to each buffer.
229 static std::unique_ptr<IOBuf> createChain(
230 size_t totalCapacity, uint32_t maxBufCapacity);
233 * Create a new IOBuf pointing to an existing data buffer.
235 * The new IOBuffer will assume ownership of the buffer, and free it by
236 * calling the specified FreeFunction when the last IOBuf pointing to this
237 * buffer is destroyed. The function will be called with a pointer to the
238 * buffer as the first argument, and the supplied userData value as the
239 * second argument. The free function must never throw exceptions.
241 * If no FreeFunction is specified, the buffer will be freed using free().
243 * The IOBuf data pointer will initially point to the start of the buffer,
245 * In the first version of this function, the length of data is unspecified
246 * and is initialized to the capacity of the buffer
248 * In the second version, the user specifies the valid length of data
251 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
252 * default) the buffer will be freed before throwing the error.
254 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
255 FreeFunction freeFn = NULL,
256 void* userData = NULL,
257 bool freeOnError = true) {
258 return takeOwnership(buf, capacity, capacity, freeFn,
259 userData, freeOnError);
262 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
264 FreeFunction freeFn = NULL,
265 void* userData = NULL,
266 bool freeOnError = true);
269 * Create a new IOBuf pointing to an existing data buffer made up of
270 * count objects of a given standard-layout type.
272 * This is dangerous -- it is essentially equivalent to doing
273 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
274 * for serialization / deserialization.
276 * The new IOBuffer will assume ownership of the buffer, and free it
277 * appropriately (by calling the UniquePtr's custom deleter, or by calling
278 * delete or delete[] appropriately if there is no custom deleter)
279 * when the buffer is destroyed. The custom deleter, if any, must never
282 * The IOBuf data pointer will initially point to the start of the buffer,
283 * and the length will be the full capacity of the buffer (count *
286 * On error, std::bad_alloc will be thrown, and the buffer will be freed
287 * before throwing the error.
289 template <class UniquePtr>
290 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
291 std::unique_ptr<IOBuf>>::type
292 takeOwnership(UniquePtr&& buf, size_t count=1);
295 * Create a new IOBuf object that points to an existing user-owned buffer.
297 * This should only be used when the caller knows the lifetime of the IOBuf
298 * object ahead of time and can ensure that all IOBuf objects that will point
299 * to this buffer will be destroyed before the buffer itself is destroyed.
301 * This buffer will not be freed automatically when the last IOBuf
302 * referencing it is destroyed. It is the caller's responsibility to free
303 * the buffer after the last IOBuf has been destroyed.
305 * The IOBuf data pointer will initially point to the start of the buffer,
306 * and the length will be the full capacity of the buffer.
308 * An IOBuf created using wrapBuffer() will always be reported as shared.
309 * unshare() may be used to create a writable copy of the buffer.
311 * On error, std::bad_alloc will be thrown.
313 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint32_t capacity);
316 * Convenience function to create a new IOBuf object that copies data from a
317 * user-supplied buffer, optionally allocating a given amount of
318 * headroom and tailroom.
320 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint32_t size,
322 uint32_t minTailroom=0);
325 * Convenience function to create a new IOBuf object that copies data from a
326 * user-supplied string, optionally allocating a given amount of
327 * headroom and tailroom.
329 * Beware when attempting to invoke this function with a constant string
330 * literal and a headroom argument: you will likely end up invoking the
331 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
332 * the first argument as a const void*, and will invoke the version of
333 * copyBuffer() above, with the size argument of 3.
335 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
337 uint32_t minTailroom=0);
340 * A version of copyBuffer() that returns a null pointer if the input string
343 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
345 uint32_t minTailroom=0);
348 * Convenience function to free a chain of IOBufs held by a unique_ptr.
350 static void destroy(std::unique_ptr<IOBuf>&& data) {
351 auto destroyer = std::move(data);
355 * Destroy this IOBuf.
357 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
358 * (See the comments above regarding the ownership model of IOBuf chains.
359 * All subsequent IOBufs in the chain are considered to be owned by the head
360 * of the chain. Users should only explicitly delete the head of a chain.)
362 * When each individual IOBuf is destroyed, it will release its reference
363 * count on the underlying buffer. If it was the last user of the buffer,
364 * the buffer will be freed.
369 * Check whether the chain is empty (i.e., whether the IOBufs in the
370 * chain have a total data length of zero).
372 * This method is semantically equivalent to
373 * i->computeChainDataLength()==0
374 * but may run faster because it can short-circuit as soon as it
375 * encounters a buffer with length()!=0
380 * Get the pointer to the start of the data.
382 const uint8_t* data() const {
387 * Get a writable pointer to the start of the data.
389 * The caller is responsible for calling unshare() first to ensure that it is
390 * actually safe to write to the buffer.
392 uint8_t* writableData() {
397 * Get the pointer to the end of the data.
399 const uint8_t* tail() const {
400 return data_ + length_;
404 * Get a writable pointer to the end of the data.
406 * The caller is responsible for calling unshare() first to ensure that it is
407 * actually safe to write to the buffer.
409 uint8_t* writableTail() {
410 return data_ + length_;
414 * Get the data length.
416 uint32_t length() const {
421 * Get the amount of head room.
423 * Returns the number of bytes in the buffer before the start of the data.
425 uint32_t headroom() const {
426 return data_ - buffer();
430 * Get the amount of tail room.
432 * Returns the number of bytes in the buffer after the end of the data.
434 uint32_t tailroom() const {
435 return bufferEnd() - tail();
439 * Get the pointer to the start of the buffer.
441 * Note that this is the pointer to the very beginning of the usable buffer,
442 * not the start of valid data within the buffer. Use the data() method to
443 * get a pointer to the start of the data within the buffer.
445 const uint8_t* buffer() const {
446 return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
450 * Get a writable pointer to the start of the buffer.
452 * The caller is responsible for calling unshare() first to ensure that it is
453 * actually safe to write to the buffer.
455 uint8_t* writableBuffer() {
456 return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
460 * Get the pointer to the end of the buffer.
462 * Note that this is the pointer to the very end of the usable buffer,
463 * not the end of valid data within the buffer. Use the tail() method to
464 * get a pointer to the end of the data within the buffer.
466 const uint8_t* bufferEnd() const {
467 return (flags_ & kFlagExt) ?
468 ext_.buf + ext_.capacity :
469 int_.buf + kMaxInternalDataSize;
473 * Get the total size of the buffer.
475 * This returns the total usable length of the buffer. Use the length()
476 * method to get the length of the actual valid data in this IOBuf.
478 uint32_t capacity() const {
479 return (flags_ & kFlagExt) ? ext_.capacity : kMaxInternalDataSize;
483 * Get a pointer to the next IOBuf in this chain.
488 const IOBuf* next() const {
493 * Get a pointer to the previous IOBuf in this chain.
498 const IOBuf* prev() const {
503 * Shift the data forwards in the buffer.
505 * This shifts the data pointer forwards in the buffer to increase the
506 * headroom. This is commonly used to increase the headroom in a newly
509 * The caller is responsible for ensuring that there is sufficient
510 * tailroom in the buffer before calling advance().
512 * If there is a non-zero data length, advance() will use memmove() to shift
513 * the data forwards in the buffer. In this case, the caller is responsible
514 * for making sure the buffer is unshared, so it will not affect other IOBufs
515 * that may be sharing the same underlying buffer.
517 void advance(uint32_t amount) {
518 // In debug builds, assert if there is a problem.
519 assert(amount <= tailroom());
522 memmove(data_ + amount, data_, length_);
528 * Shift the data backwards in the buffer.
530 * The caller is responsible for ensuring that there is sufficient headroom
531 * in the buffer before calling retreat().
533 * If there is a non-zero data length, retreat() will use memmove() to shift
534 * the data backwards in the buffer. In this case, the caller is responsible
535 * for making sure the buffer is unshared, so it will not affect other IOBufs
536 * that may be sharing the same underlying buffer.
538 void retreat(uint32_t amount) {
539 // In debug builds, assert if there is a problem.
540 assert(amount <= headroom());
543 memmove(data_ - amount, data_, length_);
549 * Adjust the data pointer to include more valid data at the beginning.
551 * This moves the data pointer backwards to include more of the available
552 * buffer. The caller is responsible for ensuring that there is sufficient
553 * headroom for the new data. The caller is also responsible for populating
554 * this section with valid data.
556 * This does not modify any actual data in the buffer.
558 void prepend(uint32_t amount) {
559 DCHECK_LE(amount, headroom());
565 * Adjust the tail pointer to include more valid data at the end.
567 * This moves the tail pointer forwards to include more of the available
568 * buffer. The caller is responsible for ensuring that there is sufficient
569 * tailroom for the new data. The caller is also responsible for populating
570 * this section with valid data.
572 * This does not modify any actual data in the buffer.
574 void append(uint32_t amount) {
575 DCHECK_LE(amount, tailroom());
580 * Adjust the data pointer forwards to include less valid data.
582 * This moves the data pointer forwards so that the first amount bytes are no
583 * longer considered valid data. The caller is responsible for ensuring that
584 * amount is less than or equal to the actual data length.
586 * This does not modify any actual data in the buffer.
588 void trimStart(uint32_t amount) {
589 DCHECK_LE(amount, length_);
595 * Adjust the tail pointer backwards to include less valid data.
597 * This moves the tail pointer backwards so that the last amount bytes are no
598 * longer considered valid data. The caller is responsible for ensuring that
599 * amount is less than or equal to the actual data length.
601 * This does not modify any actual data in the buffer.
603 void trimEnd(uint32_t amount) {
604 DCHECK_LE(amount, length_);
611 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
614 data_ = writableBuffer();
619 * Ensure that this buffer has at least minHeadroom headroom bytes and at
620 * least minTailroom tailroom bytes. The buffer must be writable
621 * (you must call unshare() before this, if necessary).
623 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
624 * the data (between data() and data() + length()) is preserved.
626 void reserve(uint32_t minHeadroom, uint32_t minTailroom) {
627 // Maybe we don't need to do anything.
628 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
631 // If the buffer is empty but we have enough total room (head + tail),
632 // move the data_ pointer around.
634 headroom() + tailroom() >= minHeadroom + minTailroom) {
635 data_ = writableBuffer() + minHeadroom;
638 // Bah, we have to do actual work.
639 reserveSlow(minHeadroom, minTailroom);
643 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
644 * if this is the only IOBuf in its chain.
646 bool isChained() const {
647 assert((next_ == this) == (prev_ == this));
648 return next_ != this;
652 * Get the number of IOBufs in this chain.
654 * Beware that this method has to walk the entire chain.
655 * Use isChained() if you just want to check if this IOBuf is part of a chain
658 uint32_t countChainElements() const;
661 * Get the length of all the data in this IOBuf chain.
663 * Beware that this method has to walk the entire chain.
665 uint64_t computeChainDataLength() const;
668 * Insert another IOBuf chain immediately before this IOBuf.
670 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
671 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
672 * and become part of the chain starting at A, which will now look like
675 * Note that since IOBuf chains are circular, head->prependChain(other) can
676 * be used to append the other chain at the very end of the chain pointed to
677 * by head. For example, if there are two IOBuf chains (A, B, C) and
678 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
679 * now consist of (A, B, C, D, E, F)
681 * The elements in the specified IOBuf chain will become part of this chain,
682 * and will be owned by the head of this chain. When this chain is
683 * destroyed, all elements in the supplied chain will also be destroyed.
685 * For this reason, appendChain() only accepts an rvalue-reference to a
686 * unique_ptr(), to make it clear that it is taking ownership of the supplied
687 * chain. If you have a raw pointer, you can pass in a new temporary
688 * unique_ptr around the raw pointer. If you have an existing,
689 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
690 * that you are destroying the original pointer.
692 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
695 * Append another IOBuf chain immediately after this IOBuf.
697 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
698 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
699 * and become part of the chain starting at A, which will now look like
702 * The elements in the specified IOBuf chain will become part of this chain,
703 * and will be owned by the head of this chain. When this chain is
704 * destroyed, all elements in the supplied chain will also be destroyed.
706 * For this reason, appendChain() only accepts an rvalue-reference to a
707 * unique_ptr(), to make it clear that it is taking ownership of the supplied
708 * chain. If you have a raw pointer, you can pass in a new temporary
709 * unique_ptr around the raw pointer. If you have an existing,
710 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
711 * that you are destroying the original pointer.
713 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
714 // Just use prependChain() on the next element in our chain
715 next_->prependChain(std::move(iobuf));
719 * Remove this IOBuf from its current chain.
721 * Since ownership of all elements an IOBuf chain is normally maintained by
722 * the head of the chain, unlink() transfers ownership of this IOBuf from the
723 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
724 * returned to the caller. The caller must store the returned unique_ptr (or
725 * call release() on it) to take ownership, otherwise the IOBuf will be
726 * immediately destroyed.
728 * Since unlink transfers ownership of the IOBuf to the caller, be careful
729 * not to call unlink() on the head of a chain if you already maintain
730 * ownership on the head of the chain via other means. The pop() method
731 * is a better choice for that situation.
733 std::unique_ptr<IOBuf> unlink() {
734 next_->prev_ = prev_;
735 prev_->next_ = next_;
738 return std::unique_ptr<IOBuf>(this);
742 * Remove this IOBuf from its current chain and return a unique_ptr to
743 * the IOBuf that formerly followed it in the chain.
745 std::unique_ptr<IOBuf> pop() {
747 next_->prev_ = prev_;
748 prev_->next_ = next_;
751 return std::unique_ptr<IOBuf>((next == this) ? NULL : next);
755 * Remove a subchain from this chain.
757 * Remove the subchain starting at head and ending at tail from this chain.
759 * Returns a unique_ptr pointing to head. (In other words, ownership of the
760 * head of the subchain is transferred to the caller.) If the caller ignores
761 * the return value and lets the unique_ptr be destroyed, the subchain will
762 * be immediately destroyed.
764 * The subchain referenced by the specified head and tail must be part of the
765 * same chain as the current IOBuf, but must not contain the current IOBuf.
766 * However, the specified head and tail may be equal to each other (i.e.,
767 * they may be a subchain of length 1).
769 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
770 assert(head != this);
771 assert(tail != this);
773 head->prev_->next_ = tail->next_;
774 tail->next_->prev_ = head->prev_;
779 return std::unique_ptr<IOBuf>(head);
783 * Return true if at least one of the IOBufs in this chain are shared,
784 * or false if all of the IOBufs point to unique buffers.
786 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
788 bool isShared() const {
789 const IOBuf* current = this;
791 if (current->isSharedOne()) {
794 current = current->next_;
795 if (current == this) {
802 * Return true if other IOBufs are also pointing to the buffer used by this
803 * IOBuf, and false otherwise.
805 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
806 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
807 * from such an IOBuf), it is always considered shared.
809 * This only checks the current IOBuf, and not other IOBufs in the chain.
811 bool isSharedOne() const {
812 if (LIKELY(flags_ & (kFlagUserOwned | kFlagMaybeShared)) == 0) {
816 // If this is a user-owned buffer, it is always considered shared
817 if (flags_ & kFlagUserOwned) {
821 // an internal buffer wouldn't have kFlagMaybeShared or kFlagUserOwned
822 // so we would have returned false already. The only remaining case
823 // is an external buffer which may be shared, so we need to read
824 // the reference count.
825 assert((flags_ & (kFlagExt | kFlagMaybeShared)) ==
826 (kFlagExt | kFlagMaybeShared));
829 ext_.sharedInfo->refcount.load(std::memory_order_acquire) > 1;
831 // we're the last one left
832 flags_ &= ~kFlagMaybeShared;
838 * Ensure that this IOBuf has a unique buffer that is not shared by other
841 * unshare() operates on an entire chain of IOBuf objects. If the chain is
842 * shared, it may also coalesce the chain when making it unique. If the
843 * chain is coalesced, subsequent IOBuf objects in the current chain will be
844 * automatically deleted.
846 * Note that buffers owned by other (non-IOBuf) users are automatically
849 * Throws std::bad_alloc on error. On error the IOBuf chain will be
852 * Currently unshare may also throw std::overflow_error if it tries to
853 * coalesce. (TODO: In the future it would be nice if unshare() were smart
854 * enough not to coalesce the entire buffer if the data is too large.
855 * However, in practice this seems unlikely to become an issue.)
866 * Ensure that this IOBuf has a unique buffer that is not shared by other
869 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
870 * unique buffer after unshareOne() returns, but other IOBufs in the chain
871 * may still be shared after unshareOne() returns.
873 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
882 * Coalesce this IOBuf chain into a single buffer.
884 * This method moves all of the data in this IOBuf chain into a single
885 * contiguous buffer, if it is not already in one buffer. After coalesce()
886 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
887 * chain will be automatically deleted.
889 * After coalescing, the IOBuf will have at least as much headroom as the
890 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
893 * Throws std::bad_alloc on error. On error the IOBuf chain will be
894 * unmodified. Throws std::overflow_error if the length of the entire chain
895 * larger than can be described by a uint32_t capacity.
905 * Ensure that this chain has at least maxLength bytes available as a
906 * contiguous memory range.
908 * This method coalesces whole buffers in the chain into this buffer as
909 * necessary until this buffer's length() is at least maxLength.
911 * After coalescing, the IOBuf will have at least as much headroom as the
912 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
913 * that was coalesced.
915 * Throws std::bad_alloc on error. On error the IOBuf chain will be
916 * unmodified. Throws std::overflow_error if the length of the coalesced
917 * portion of the chain is larger than can be described by a uint32_t
918 * capacity. (Although maxLength is uint32_t, gather() doesn't split
919 * buffers, so coalescing whole buffers may result in a capacity that can't
920 * be described in uint32_t.
922 * Upon return, either enough of the chain was coalesced into a contiguous
923 * region, or the entire chain was coalesced. That is,
924 * length() >= maxLength || !isChained() is true.
926 void gather(uint32_t maxLength) {
927 if (!isChained() || length_ >= maxLength) {
930 coalesceSlow(maxLength);
934 * Return a new IOBuf chain sharing the same data as this chain.
936 * The new IOBuf chain will normally point to the same underlying data
937 * buffers as the original chain. (The one exception to this is if some of
938 * the IOBufs in this chain contain small internal data buffers which cannot
941 std::unique_ptr<IOBuf> clone() const;
944 * Return a new IOBuf with the same data as this IOBuf.
946 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
947 * part of a larger chain).
949 std::unique_ptr<IOBuf> cloneOne() const;
952 * Return an iovector suitable for e.g. writev()
954 * auto iov = buf->getIov();
955 * auto xfer = writev(fd, iov.data(), iov.size());
957 * Naturally, the returned iovector is invalid if you modify the buffer
960 folly::fbvector<struct iovec> getIov() const;
962 // Overridden operator new and delete.
963 // These directly use malloc() and free() to allocate the space for IOBuf
964 // objects. This is needed since IOBuf::create() manually uses malloc when
965 // allocating IOBuf objects with an internal buffer.
966 void* operator new(size_t size);
967 void* operator new(size_t size, void* ptr);
968 void operator delete(void* ptr);
971 * Destructively convert this IOBuf to a fbstring efficiently.
972 * We rely on fbstring's AcquireMallocatedString constructor to
975 fbstring moveToFbString();
978 * Iteration support: a chain of IOBufs may be iterated through using
979 * STL-style iterators over const ByteRanges. Iterators are only invalidated
980 * if the IOBuf that they currently point to is removed.
982 Iterator cbegin() const;
983 Iterator cend() const;
984 Iterator begin() const;
985 Iterator end() const;
988 enum FlagsEnum : uint32_t {
990 kFlagUserOwned = 0x2,
991 kFlagFreeSharedInfo = 0x4,
992 kFlagMaybeShared = 0x8,
995 // Values for the ExternalBuf type field.
996 // We currently don't really use this for anything, other than to have it
997 // around for debugging purposes. We store it at the moment just because we
998 // have the 4 extra bytes in the ExternalBuf struct that would just be
999 // padding otherwise.
1000 enum ExtBufTypeEnum {
1002 kExtUserSupplied = 1,
1008 SharedInfo(FreeFunction fn, void* arg);
1010 // A pointer to a function to call to free the buffer when the refcount
1011 // hits 0. If this is NULL, free() will be used instead.
1012 FreeFunction freeFn;
1014 std::atomic<uint32_t> refcount;
1016 struct ExternalBuf {
1020 // SharedInfo may be NULL if kFlagUserOwned is set. It is non-NULL
1021 // in all other cases.
1022 SharedInfo* sharedInfo;
1024 struct InternalBuf {
1025 uint8_t buf[] __attribute__((aligned));
1028 // The maximum size for an IOBuf object, including any internal data buffer
1029 static const uint32_t kMaxIOBufSize = 256;
1030 static const uint32_t kMaxInternalDataSize;
1032 // Forbidden copy constructor and assignment opererator
1033 IOBuf(IOBuf const &);
1034 IOBuf& operator=(IOBuf const &);
1037 * Create a new IOBuf with internal data.
1039 * end is a pointer to the end of the IOBuf's internal data buffer.
1041 explicit IOBuf(uint8_t* end);
1044 * Create a new IOBuf pointing to an external buffer.
1046 * The caller is responsible for holding a reference count for this new
1047 * IOBuf. The IOBuf constructor does not automatically increment the
1050 IOBuf(ExtBufTypeEnum type, uint32_t flags,
1051 uint8_t* buf, uint32_t capacity,
1052 uint8_t* data, uint32_t length,
1053 SharedInfo* sharedInfo);
1055 void unshareOneSlow();
1056 void unshareChained();
1057 void coalesceSlow(size_t maxLength=std::numeric_limits<size_t>::max());
1058 // newLength must be the entire length of the buffers between this and
1059 // end (no truncation)
1060 void coalesceAndReallocate(
1064 size_t newTailroom);
1065 void decrementRefcount();
1066 void reserveSlow(uint32_t minHeadroom, uint32_t minTailroom);
1068 static size_t goodExtBufferSize(uint32_t minCapacity);
1069 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1070 SharedInfo** infoReturn,
1071 uint32_t* capacityReturn);
1072 static void allocExtBuffer(uint32_t minCapacity,
1073 uint8_t** bufReturn,
1074 SharedInfo** infoReturn,
1075 uint32_t* capacityReturn);
1082 * Links to the next and the previous IOBuf in this chain.
1084 * The chain is circularly linked (the last element in the chain points back
1085 * at the head), and next_ and prev_ can never be NULL. If this IOBuf is the
1086 * only element in the chain, next_ and prev_ will both point to this.
1092 * A pointer to the start of the data referenced by this IOBuf, and the
1093 * length of the data.
1095 * This may refer to any subsection of the actual buffer capacity.
1099 mutable uint32_t flags_;
1106 struct DeleterBase {
1107 virtual ~DeleterBase() { }
1108 virtual void dispose(void* p) = 0;
1111 template <class UniquePtr>
1112 struct UniquePtrDeleter : public DeleterBase {
1113 typedef typename UniquePtr::pointer Pointer;
1114 typedef typename UniquePtr::deleter_type Deleter;
1116 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1117 void dispose(void* p) {
1119 deleter_(static_cast<Pointer>(p));
1130 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1131 static_cast<DeleterBase*>(userData)->dispose(ptr);
1135 template <class UniquePtr>
1136 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1137 std::unique_ptr<IOBuf>>::type
1138 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1139 size_t size = count * sizeof(typename UniquePtr::element_type);
1140 DCHECK_LT(size, size_t(std::numeric_limits<uint32_t>::max()));
1141 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1142 return takeOwnership(buf.release(),
1144 &IOBuf::freeUniquePtrBuffer,
1148 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1149 const void* data, uint32_t size, uint32_t headroom,
1150 uint32_t minTailroom) {
1151 uint32_t capacity = headroom + size + minTailroom;
1152 std::unique_ptr<IOBuf> buf = create(capacity);
1153 buf->advance(headroom);
1154 memcpy(buf->writableData(), data, size);
1159 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1161 uint32_t minTailroom) {
1162 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1165 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1167 uint32_t minTailroom) {
1171 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1174 class IOBuf::Iterator : public boost::iterator_facade<
1175 IOBuf::Iterator, // Derived
1176 const ByteRange, // Value
1177 boost::forward_traversal_tag // Category or traversal
1179 friend class boost::iterator_core_access;
1181 // Note that IOBufs are stored as a circular list without a guard node,
1182 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1183 // the ambiguity (at the cost of one extra comparison in the "increment"
1184 // code path), we define end iterators as having pos_ == end_ == nullptr
1185 // and we only allow forward iteration.
1186 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1189 // Sadly, we must return by const reference, not by value.
1197 val_ = ByteRange(pos_->data(), pos_->tail());
1200 void adjustForEnd() {
1202 pos_ = end_ = nullptr;
1209 const ByteRange& dereference() const {
1213 bool equal(const Iterator& other) const {
1214 // We must compare end_ in addition to pos_, because forward traversal
1215 // requires that if two iterators are equal (a == b) and dereferenceable,
1217 return pos_ == other.pos_ && end_ == other.end_;
1221 pos_ = pos_->next();
1230 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1231 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1235 #pragma GCC diagnostic pop
1237 #endif // FOLLY_IO_IOBUF_H_